摘要：
内存屏障，可以保证在此之前的代码全部执行完才开始执行在此之后的代码参考wikipedia的定义：Memory barrier, also known as membar or memory fence or fence instruction, is a type of barrier and a class of instruction which causes a central processing unit (CPU) or compiler to enforce an ordering constraint on memory operations issued before and 阅读全文
